ADAMTS-13 mutant

ABSTRACT

An enhanced disintegrin-like domain, and metalloprotease, with an isolated human thrombospondin type 1 motif, member 13 (ADAMTS-13) that includes substitutions at one or more positions in the isolated human ADAMTS-13.

This application is a divisional application of U.S. application Ser. No. 14/166,177, allowed, which was a divisional application of U.S. application Ser. No. 12/666,051, now U.S. Pat. No. 8,685,665, and incorporated herein by reference, which was a National Stage of PCT/JP08/061211 filed Jun. 19, 2008 and claims the benefit of JP 2007-164531 filed Jun. 22, 2007, JP 2008-020012 filed Jan. 31, 2008, and JP 2008-020177 filed Jan. 31, 2008.

TECHNICAL FIELD

The present invention relates to a mutant of ADAMTS-13 which is an enzyme capable of cleaving von Willebrand factor (hereinafter referred to as “VWF”) at Tyr-Met site in A2 domain. Specifically, the present invention relates to a method of preparing ADAMTS-13 mutant having an enhanced enzymatic activity or a reduced reactivity to a neutralizing autoantibody by substituting amino acid residues specific to ADAMTS-13. In addition, the present invention relates to a mutant obtained by said method, a pharmaceutical composition comprising as an active ingredient said mutant, and a pharmaceutical preparation for treating thrombosis comprising said pharmaceutical composition.

BACKGROUND ART

ADAMTS-13 is a zinc-metalloprotease belonging to ADAMTS (a disintegrin-like domain, and metalloprotease, with thrombospondin type 1 motif) family and specifically cleaves von Willebrand factor (VWF) at Tyr1605-Met1606, which corresponds to 842-843 after cleavage of a preprosequence (VWF cleavage enzyme: VWF-Cleaving Protease, VWF-CP)(see e.g. Non-patent reference 1). ADAMTS-13 is known to be an activity modulation factor of VWF that is an important factor of platelet aggregation. VWF released through stimulation or circulating in blood is important in forming platelet thrombus because it plays a role as a collaboration with collagen on platelet adhesion and agglutination in the subendothelial tissue of a damaged vascular wall (e.g. see Non-patent reference 2).

It is considered that VWF is subjected to conformational change by intravascular shear force in blood circulation to thereby expose A2 domain, and Tyr1605-Met1606 therein, ADAMTS-13 cleavage site, is rapidly hydrolyzed by ADAMTS-13. Anderson et et al. evaluated a catalytic efficiency of ADAMTS-13 using as a substrate VWF previously subjected to guanidinium hydrochloride to induce the conformational change (see e.g. Non-patent reference 3). The result showed that kcat was up to 0.83 min⁻¹ and kcat/Km was 55 μM⁻¹ min⁻¹, which are lower than those of the other enzymes of a coagulation system to natural high molecular weight substrates, indicating that ADAMTS-13 has a lower enzymatic activity.

Thrombotic thrombocytopenic purpura (hereinafter also referred to as “TTP”) caused by a reduced activity of ADAMTS-13 is classified into a congenital TTP and an acquired TTP. The congenital TTP is hereditary and caused by a molecular abnormality of ADAMTS-13 (also called Upshow Schulmann syndrome (USS)) and the acquired TTP is positive in a neutralizing autoantibody to ADAMTS-13. While a plasma transfusion is currently conducted to supplement ADAMTS-13 for treating the congenital TTP, it is desired that an ADAMTS-13 concentrate or a recombinant formulation is alternatively used for said treating in future. Moreover, a plasmapheresis is generally conducted to both remove the neutralizing antibody and to supplement ADAMTS-13 for treating the acquired TTP.

It has often reported that the molecular abnormality of ADAMTS-13 is found in patients with congenital TTP (USS) wherein a missense and/or nonsense mutation is found throughout the molecule. However, the pathogenesis of TTP starting in adult are also found, suggesting that possibly the congenital reduced ADAMTS-13 is not the only trigger of the pathogenesis of TTP. Considering that there are cases of the pathogenesis of congenital TTP during a pregnancy (VWF in blood may increase to 300% of the normal value during late pregnancy), the systemic platelet thrombus formation arising from TTP may be caused by the increased VWF in blood induced by the second trigger such as an environment factor or a genetic factor in addition to the reduced ADAMTS-13 in blood. Indeed, the present inventors have found that a re-event rate of acute myocardial infarction (hereinafter also referred to as “AMI”) within 1 year is significantly high when the ratio between VWF and ADAMTS-13 in blood (VWF/ADAMTS-13) after 24 hours of the onset of AMI exceeds a certain value (see e.g. Patent reference 1).

In addition, an ADAMTS-13 antigen level in plasma of patients with thrombotic disease, including disseminated intravascular coagulation (DIC), hemolytic-uremic syndrome (HUS), deep vein thrombosis (DVT), TTP, pulmonary embolism, cerebral infarction and systemic lupus erythematosus (SLE), is significantly reduced compared to healthy adult (see e.g. Patent reference 2), wherein an ADAMTS-13 antigen level is measured with sandwich ELISA using a monoclonal antibody. Moreover, with respect to DIC associated with septicemia, it was shown that patients having ADAMTS-13 blood level of less than 20% is significantly likely to develop nephropathy as compared to patients having ADAMTS-13 blood level of 20% or more (see e.g. Non-patent reference 4).

Meanwhile, endothelial cells stimulated by inflammatory cytokine, IL-8 and/or TNF-α, induce a release of unusually large (UL) VWF that has a larger multimer structure than normal. There is also an experimental result that IL-6 inhibits a VWF cleaving activity of ADSAMTS-13 under a shear stress of blood Flow (ex vivo). Therefore, it is suggested that there is an association between inflammation and thrombus formation (see e.g. Non-patent reference 5).

In addition, it is reported that ciga toxin which causes HUS stimulates vascular endothelial cells to promote ULVWF release and inhibits the activity of ADAMTS-13. It seems possible that HUS is improved by administering ADAMTS-13 to patients with HUS (see e.g. Non-patent reference 6). Thus, when the disease as stated above may be aggravated due to an imbalance involving the reduced ADAMTS-13 and the elevated VWF, administration of ADAMTS-13 may alleviate the condition of the disease.

ADAMTS-13 as previously described belongs to a metalloprotease group called ADAMTS family. ADAMTS-1 to -20 are known as a member of this family (ADAMTS-5 is identical to ADAMTS-11). ADAMTS-13 as well as the other members of ADAMTS family has a multidomain structure (FIG. 1). The amino acid sequence of ADAMTS-13 is encoded by a DNA which contains 4284 bases and ranges from a start codon ATG(Met) to a stop codon TGA. An ADAMTS-13 gene has 29 Exons on the chromosome 9q34 and 37 kb in full-length. It is revealed via the gene sequencing of ADAMTS-13 protein that ADAMTS-13 protein has 1427 amino acid residues in the precursor thereof and 10 asparagine-linked glycosylation potential sites and is a large single-strand glycoprotein (Patent reference 4).

In a process of biosynthesis, a preprosequence of 74 residues is cleaved by a processing endoprotease Furin to provide a mature form containing 1353 amino acid residues. RQRR sequence (SEQ ID NO: 80), a cleaved motif of Furin, at the end of preprosequence is followed by a metalloprotease domain that contains a Reprolysin type zinc chelate domain comprising a consensus sequence HEXXHXXGXXHD (SEQ ID NO: 81). Then, via a disintegrin-like domain which is found in a snake venom metalloprotease, there follows the first Tsp1 motif (Tsp1-1) consisting of about 50 to 60 residues which is generally thought to be important for a molecular recognition and then a cysteine-rich domain containing one of a cell adherence motif, Arg-Gly-Asp (RGD) sequence. A spacer domain containing about 130 amino acid residues without cysteine residue then follows, and again Tsp1 motif is repeated (Tsp1-2 to Tsp1-8) followed by CUB 1 and 2 domains that have firstly been found in complement components Clr or Cls. These CUB domains are characteristic of ADAMTS-13 because among ADAMTS family only ADAMTS-13 has these domains. The present inventors have previously identified from the metalloprotease domain to spacer domain of ADAMTS-13 as domains essential for exerting an enzymatic activity or as an epitope for antibody neutralization (see e.g. Patent reference 3, and Non-patent references 7 and 8).

-   Patent reference 1: JP-A-2007-248395 -   Patent reference 2: WO2005/062054 -   Patent reference 3: WO2004/029242 -   Patent reference 4: WO2002/088366 -   Non-patent reference 1: Soejima, K., Mimura, N., Hirashima, M.,     Maeda, H., Hamamoto, T., Nakagaki, T. & Nozaki, C.: A novel human     metalloprotease synthesized in the liver and secreted into the     blood: possibly, the von Willebrand factor-cleaving protease? J.     Biochem., 130: p. 475-480, 2001 -   Non-patent reference 2: Soejima, K. & Nakagaki, T.: Interplay     between ADAMTS13 and von Willebrand factor in inherited and acquired     thrombotic microangiopathies. Semin. Hematol., 42: p. 56-62, 2005 -   Non-patent reference 3: Anderson, P. J., Kokame, K. & Sadler, J. E.:     Zinc and calcium ions cooperatively modulate ADAMTS13 activity. J.     Biol. Chem., 281: p. 850-857, 2006 Non-patent reference 4: Ono, T.,     Mimuro, J., Madoiwa, S., Soejima, K., Kashiwakura, Y., Ishiwata, A.,     Takano, K., Ohmori, T. & Sakata, Y.: Severe secondary deficiency of     von Willebrand factor-cleaving protease (ADAMTS13) in patients with     sepsis-induced disseminated intravascular coagulation: its     correlation with development of renal failure. Blood, 107: p.     528-534, 2006 -   Non-patent reference 5: Bernardo, A., Ball, C., Nolasco, L.,     Moake, J. F. & Dong, J. F.: Effects of inflammatory cytokines on the     release and cleavage of the endothelial cell-derived ultralarge von     Willebrand factor multimers under flow. Blood, 104: p. 100-106, 2004 -   Non-patent reference 6: Nolasco, L. H., Turner, N. A., Bernardo, A.,     Tao, Z., Cleary, T. G., Dong, J. F. & Moake, J. L.: Hemolytic uremic     syndrome-associated Shiga toxins promote endothelial-cell secretion     and impair ADAMTS13 cleavage of unusually large von Willebrand     factor multimers. Blood, 106: p. 4199-4209, 2005 -   Non-patent reference 7: Soejima, K., Matsumoto, M., Kokame, K.,     Yagi, H., Ishizashi, H., Maeda, H., Nozaki, C., Miyata, T.,     Fujimura, Y. & Nakagaki, T.: ADAMTS-13 cysteine-rich/spacer domains     are functionally essential for von Willebrand factor cleavage.     Blood, 102: p. 3232-3237, 2003 -   Non-patent reference 8: Soejima, K., Nakamura, H., Hirashima, M.,     Morikawa, W., Nozaki, C. & Nakagaki, T.: Analysis on the molecular     species and concentration of circulating ADAMTS13 in blood. J.     Biochem., 139: p. 147-154, 2006

DISCLOSURE OF THE INVENTION

(Technical Problem to be Solved by the Invention)

Thus, the present invention enables the broad application as described above by preparing ADAMTS-13 mutant having a higher activity. Moreover, the mutant which has a reduced reactivity to a neutralizing antibody while holding the enzymatic activity may be applied to the acquired TTP. ADAMTS-13 mutant having such properties has never been reported so far.

Therefore, the technical problem to be solved by the present invention is to provide ADAMTS-13 mutant having an efficiently high activity for treating TTP etc. or a reduced reactivity to a neutralizing antibody.

(Means for Solving the Problems)

Under these circumstances, the present inventors have earnestly studied to develop ADAMTS-13 mutant having a high enzymatic activity or the mutant maintaining the enzymatic activity while the reactivity thereof with a neutralizing antibody is reduced by altering an epitope for a neutralizing antibody to thereby complete the present invention. The present inventors have succeeded in preparing ADAMTS-13W688X protein mutant which has an enhanced enzymatic activity or a reduced reactivity with a neutralizing antibody (hereinafter also referred to as “ADAMTS-13 mutant”) by substitution of an amino acid contained in the disintegrin-like domain, the cysteine-rich domain or the spacer domain of a C-terminal deletion mutant W688X. Said C-terminal deletion mutant W688X (hereinafter also referred to as “ADAMTS-13W688X protein”; see Patent reference 3 and Non-patent reference 7) is a minimum unit of ADAMTS-13 exerting the activity and is provided by deleting amino acid residues ranging from the 689th amino acid to the C terminus from the 1427 amino acid residues. That is, the present invention is as described below. In addition, the modification according to the present invention may also be accomplished using a full-length of ADAMTS-13 (wild type strain) molecule.

(1) ADAMTS-13 mutant wherein at least one charged amino acid in a disintegrin-like domain, a cysteine-rich domain or a spacer domain of ADAMTS-13 other than the following amino acids is substituted with a different amino acid: arginine at position 326, aspartic acid at position 330, aspartic acid at position 343 and arginine at position 349 in the disintegrin-like domain, aspartic acid at position 480, arginine at position 488, arginine at position 498, arginine at position 507, aspartic acid at position 533 and aspartic acid at position 543 in the cysteine-rich domain, and glutamic acid at position 641 and arginine at position 660 in the spacer domain.

(2) The mutant according to (1) wherein said different amino acid is an uncharged amino acid.

(3) The mutant according to (1) or (2) wherein the charged amino acid to be substituted is an amino acid present in or around the neutralizing antibody recognition epitope including at least one of arginine at position 312, lysine at position 318, arginine at position 568, glutamic acid at position 569, arginine at position 589, lysine at position 608, glutamic acid at position 634 or aspartic acid at position 635.

(4) The mutant according to (1) or (2) wherein the charged amino acid to be substituted is selected from the group consisting of aspartic acid at position 298, arginine at position 312, arginine at position 326, glutamic acid at position 327, arginine at position 370, arginine at position 452, aspartic acid at position 504, arginine at position 514, aspartic acid at position 537, arginine at position 568 and arginine at position 659.

(5) The mutant according to any one of (2)-(4) wherein the uncharged amino acid is selected from the group consisting of alanine, glycine, proline, serine and threonine.

(6) A method of enhancing an enzymatic activity of ADAMTS-13 wherein at least one charged amino acid in a disintegrin-like domain, a cysteine-rich domain or a spacer domain of ADAMTS-13 other than the following amino acids is substituted with a different amino acid: arginine at position 326, aspartic acid at position 330, aspartic acid at position 343 and arginine at position 349 in the disintegrin-like domain, aspartic acid at position 480, arginine at position 488, arginine at position 498, arginine at position 507, aspartic acid at position 533 and aspartic acid at position 543 in the cysteine-rich domain, and glutamic acid at position 641 and arginine at position 660 in the spacer domain.

(7) A method of reducing a reactivity of ADAMTS-13 to an anti-ADAMTS-13 neutralizing antibody, wherein at least one charged amino acid in a disintegrin-like domain, a cysteine-rich domain or a spacer domain of ADAMTS-13 other than the following amino acids is substituted with a different amino acid: arginine at position 326, aspartic acid at position 330, aspartic acid at position 343 and arginine at position 349 in the disintegrin-like domain, aspartic acid at position 480, arginine at position 488, arginine at position 498, arginine at position 507, aspartic acid at position 533 and aspartic acid at position 543 in the cysteine-rich domain, and glutamic acid at position 641 and arginine at position 660 in the spacer domain.

(8) The method according to (6) or (7) wherein the different amino acid is an uncharged amino acid.

(9) The method according to any one of (6)-(8) wherein the charged amino acid to be substituted is present in or around the neutralizing antibody recognition epitope, including at least one of arginine at position 312, lysine at position 318, arginine at position 568, glutamic acid at position 569, arginine at position 589, lysine at position 608, glutamic acid at position 634, aspartic acid at position 635 or arginine at position 639.

(10) The method according to any one of (6)-(8) wherein the charged amino acid to be substituted is selected from the group consisting of aspartic acid at position 298, arginine at position 312, arginine at position 326, glutamic acid at position 327, arginine at position 370, arginine at position 452, aspartic acid at position 504, arginine at position 514, aspartic acid at position 537, arginine at position 568 and arginine at position 659.

(11) The method according to any one of (8)-(10) wherein the uncharged amino acid is selected from the group consisting of alanine, glycine, proline, serine and threonine.

(12) A pharmaceutical composition containing as an active ingredient the ADAMTS-13 mutant of any one of (1)-(5).

(13) A therapeutic agent for thrombotic disease comprising as an active ingredient the ADAMTS-13 mutant of any one of (1)-(5).

(14) The therapeutic agent according to (13) wherein the thrombotic disease is disseminated intravascular coagulation (DIC), hemolytic-uremic syndrome (HUS), deep vein thrombosis (DVT), thrombotic thrombocytopenic purpura (TTP), myocardial infarction, pulmonary embolism, cerebral infarction or systemic lupus erythematosus (SLE).

Effects of the Invention

The present invention provides a method of preparing ADAMTS-13 mutant having a high enzymatic activity and the ADAMTS-13 mutant obtained by said method. For example, ADAMTS-13 mutant is provided by substituting at least one of charged amino acids present in the disintegrin-like domain, the cysteine-rich domain or the spacer domain with an uncharged amino acid. Moreover, ADAMTS-13 mutant having a reduced reactivity to a neutralizing antibody in addition to the high enzymatic activity is provided by substituting a charged amino acid present in or around the epitope for an anti-ADAMTS-13 neutralizing antibody with an uncharged amino acid. Therefore, ADAMTS-13 mutant of the present invention may be a useful active ingredient for treating patients with thrombosis and expected to provide a good effect with a small dosage. The term of “uncharged amino acid” as used herein refers to all of the amino acids other than charged amino acids (lysine, arginine, glutamic acid and aspartic acid).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a gene structure and a protein domain structure of ADAMTS-13. Black dots indicate 10 N-linked glycosylation potential sites. FIG. 1 discloses “RQRR” as SEQ ID NO: 80.

FIG. 2 shows the results of Western blot for culture supernatant of ADAMTS-13 mutant.

FIG. 3 shows evaluation of a cleaving activity of ADAMTS-13 mutant to a synthetic substrate FRETS-VWF73. The specific activity (U=units/μg) is shown as a hydrolytic activity of the mutant (units) per the amount of protein of the mutant (the amount of antigen) (μg). The relative activity (Umutant/Uwt) was obtained from a ratio of the specific activity of the mutant to that of the wild type strain (U=U(mutant)/U(wild type strain)). The specific activity (U=units/μg); U=the hydrolytic activity of the mutant (units)/the amount of protein of the mutant (the amount of antigen)(μg). The relative activity (Umutant/Uwt); U mutant/U wild type strain.

FIG. 4 shows evaluation of a cleaving activity of ADAMTS-13 mutant to a natural substrate VWF. The specific activity (U=units/μg) is shown as the hydrolytic activity of the mutant (units) per the amount of protein of the mutant (the amount of antigen)(μg). The relative activity (Umutant/Uwt) was obtained from a ratio of the specific activity of the mutant to that of the wild type strain (U=U mutant/U wild type strain). The specific activity (U=units/μg); U=the hydrolytic activity of the mutant (units)/the amount of protein of the mutant (the amount of antigen)(μg). The relative activity (Umutant/Uwt); U mutant/U wild type strain.

FIG. 5 shows evaluation of a binding ability of ADAMTS-13 mutant to VWF immobilized on ELISA plate. The specific activity (U=units/μg) is shown as the binding activity of the mutant (units) per the amount of protein of the mutant (the amount of antigen)(μg). The relative activity (Umutant/Uwt) was obtained from a ratio of the specific activity of mutant to that of the wild type strain (U=U mutant/U wild type strain). The specific activity (U=units/μg); U=the binding activity of the mutant (units)/the amount of protein of the mutant (the amount of antigen)(μg). The relative activity (Umutant/Uwt); U mutant/U wild type strain.

FIG. 6 shows the results of Western blot for an epitope analysis of a neutralizing murine monoclonal antibody. The arrows indicate the estimated epitope amino acids.

FIG. 7 shows the results of Western blot for an epitope analysis of an autoantibody of acquired TTP patient A. The arrows indicate the estimated epitope amino acids.

FIG. 8 shows the results of Western blot for an epitope analysis of an autoantibody of acquired TTP patient B. The arrows indicate the estimated epitope amino acids.

FIG. 9 shows the results of Western blot for an epitope analysis of an autoantibody of acquired TTP patient C. The arrows indicate the estimated epitope amino acids.

FIG. 10 shows evaluation of the cleaving activity of ADAMTS-13 mutant which has a reduced reactivity to an acquired TTP autoantibody to the synthetic substrate FRETS-VWF73.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is characterized by a method of enhancing an enzymatic activity of ADAMTS-13 and/or a method of reducing the reactivity to an anti-ADAMTS-13 neutralizing antibody as well as a mutant of ADAMTS-13 prepared by said methods. The method of the present invention is accomplished by substituting a charged amino acid (arginine (R), lysine (K), glutamic acid (E), aspartic acid (D)) in the disintegrin-like domain, the cysteine-rich domain or the spacer domain with a different amino acid, especially an uncharged amino acid on the basis of the minimum unit of ADAMTS-13 exerting the activity (ADAMTS-13W688X protein), and evaluating the enzymatic activity of the resulting mutant and the reactivity thereof to a neutralizing monoclonal antibody. Detail of the method is described herein below.

The gene W688X encoding the minimum unit of ADAMTS-13 exerting the activity (hereinafter also referred to as “ADAMTS-13W688X gene”) may be obtained, for example, by designing a PCR primer on the basis of the sequence as described in Non-patent reference 7 and Patent reference 3 and conducting PCR using as a template cDNA derived from human organs or cells producing ADAMTS-13. In particular, the ADAMTS-13W688X gene may be prepared as described below. First, total RNAs are extracted from human hepatocytes and then mRNAs are purified therefrom. The resulting mRNAs are converted to cDNAs, then PCR reaction is conducted using PCR primers designed depending on each of the gene sequences, and the resulting PCR products are incorporated into a plasmid vector which is introduced into E. coli. The clone containing cDNA encoding the desired protein is chosen among E. coli colonies. For the extraction of total RNAs, commercially available reagents such as TRIzol reagent (GIBCO BRL) and ISOGEN (NIPPON GENE Co., Ltd.) may be used. For the purification of mRNAs, commercially available kits such as mRNA Purification Kit (Amersham BioSciences) may be used. For the conversion to cDNAs, commercially available kits for preparing cDNA library such as SuperScript plasmid system for cDNA synthesis and plasmid cloning (GIBCO BRL) may be used. For practically obtaining the ADAMTS-13W688X gene, a commercially available cDNA library such as e.g. Human Liver Marathon-Ready cDNA (BC Bioscience) may be used. The PCR primers are readily available from companies in charge of DNA synthesis (e.g. QIAGEN). It is preferred that KOZAK sequence (Kozak M, J. Mol. Biol., 196, 947 (1987)) and an adequate sequence of a restriction enzyme cleavage site is added to the 5′ side of the primer. The PCR reaction may be conducted using a commercially available Advantage HF-2 PCR Kit (BC Bioscience) in accordance with the appended protocol. The base sequence of DNA fragments obtained from PCR is determined by a DNA sequencer, e.g. CEQ2000XL DNA Analysis System (Beckman) after the cloning using a TA cloning kit (Invitrogen Corporation) etc.

In order to introduce a point mutation to the resulting ADAMTS-13W688X gene, site-directed mutagenesis may generally be used. Practically, the introduction of a point mutation to the ADAMTS-13W688X gene is conducted using a commercially available kit such as Site-Directed Mutagenesis System (Takara: Mutan-Super Express Km, Mutan-Express Km, Mutan-K and the like), QuickChange Multi Site-Directed Mutagenesis Kit, QuickChange XL Site-Directed Mutagenesis Kit (Stratagene) and GeneTailor Site-Directed Mutagenesis System (Invitrogen) applying said technique in accordance with the appended protocol. A total of 78 primers as listed in Table 1 may be used in order to substitute any of the charged amino acids, N-linked glycosylation potential sites in the disintegrin-like domain, the cysteine-rich domain, and the spacer domain of ADAMTS-13 with alanine. Multiple point mutations may be introduced by repeating site-directed mutagenesis using as a template the ADAMTS-13W688X gene where a point mutation is introduced and different primers. A DNA sequence of the ADAMTS-13W688X gene where a point mutation is introduced may be determined by the above DNA sequencer.

The ADAMTS-13W688X gene or the ADAMTS-13W688X gene with a point mutation (hereinafter also referred to as “altered ADAMTS-13W688X gene”) may be incorporated into an appropriate expression vector and a host may be transformed with said expression vector to allow for expression of the minimum unit of ADAMTS-13 exerting the activity (ADAMTS-13W688X protein) and the mutant thereof (ADAMTS-13 mutant). As a host, a bacterial cell, a yeast cell, an animal cell, a plant cell and an insect cell etc. may be used as commonly used to express a foreign protein as long as efficacy as a therapeutic agent for thrombotic disease is exhibited. Preferably, a eukaryotic cell such as an animal cell may be used. When an animal cell is used as a host, an expression vector may be incorporated with a promoter and marker genes for selection and for gene amplification depending on the host animal cell as used. For example, for an expression vector constructed using an expression plasmid containing chicken β-actin promoter (pCAGG vector), HeLa cell, 293 cell, CHO cell, or BHK cell may be used.

The known method may be used to transform a host cell. For example, the use of calcium phosphate, the use of DEAE dextran, the method using liposomes of Lipofectin, protoplast polyethylene glycol fusion, electroporation, and the like may be employed and appropriately be selected depending on a host cell as used (Molecular Cloning (3rd Ed.), Vol. 3, Cold Spring Harbor Laboratory Press (2001)).

Selection and proliferation of the transformed cells may be performed by a method as usually used for transformation of animal cells. For example, the cells after transformation may be cultured using a selection medium at 37° C. for 10-14 days while appropriately exchanging the culture medium. The selection medium includes a medium generally used to cultivate animal cells such as a serum-free medium, e.g. CHO-S-SFMII medium (GIBCO-BRL), IS CHO-V medium (IS Japan Co., Ltd.), YMM medium or a serum medium, e.g. MEM a medium, RPMI medium or Dulbecco MEM medium (all from GIBCO-BRL) supplemented with about 5-10% fetal bovine serum. The selection medium may contain methotrexate, G418, and the like depending on the employed selection marker. Upon the culture, untransformed cells are not alive and only transformed cells are grown. In addition, the transformed cells are subjected to limiting dilution etc. to select and clone cell strains of interest producing the ADAMTS-13W688X protein or the ADAMTS-13 mutant.

To purify the ADAMTS-13W688X protein or the ADAMTS-13 mutant from the cells producing said protein, a purification method generally used in the protein chemistry may be used. The purification method includes, for example, centrifugation, salting-out, ultrafiltration, isoelectric precipitation, electrophoresis, ion-exchange chromatography, gel filtration, affinity chromatography, hydrophobic chromatography, hydroxyapatite chromatography and CS resin chromatography in combination thereof. An amount of the obtained protein may be determined using a reagent for protein measurement such as BCA Protein Assay Reagent Kit (Pierce Biotechnology, Inc), Protein Assay Kit (BIO-RAD, Inc), and the like.

The ADAMTS-13W688X protein or the ADAMTS-13 mutant may be expressed in the form of a fusion with other polypeptide or peptide to allow for easier purification. A vector expressing such a fusion protein includes the system which may express a fusion protein associated with FLAG tag (SIGMA), a GST fusion protein purification system which can prepare a fusion protein with glutathione S transferase (GST) (Amersham Pharmacia), an HAT protein expression/purification system (Clontech Inc.) which is capable of adding oligohistidine, Magne His Protein Purification System (Promega Inc), and the like. For example, as described in Examples of the present invention, the ADAMTS-13 mutant expression product expressed as a fusion protein with FLAG tag is specifically purified using agarose gel immobilized with an anti-FLAGM2 monoclonal antibody (SIGMA CORPORATION). The detection of the ADAMTS-13W688X protein or the ADAMTS-13 mutant may be conducted by a method on the basis of a molecular size such as SDS-PAGE, gel filtration, and the like or a method on the basis of an antigen-antibody reaction such as ELISA, Western blot, dot blot, and the like. The above methods are all commonly used to determine a foreign protein and may be selected in accordance with the purpose.

To evaluate the ability of the ADAMTS-13 mutant as an enzyme, the activity to bind to or degrade von Willebrand factor (VWF) derived from human plasma or partially synthesized peptide of VWF may be measured by a method such as ELISA and the like using an antibody to ADAMTS-13 or an antibody to FLAG and compared to the activity of a wild-type ADAMTS-13W688X protein with no amino acid substitution. ELISA may be constructed by a common procedure. VWF derived from human plasma and an antibody to ADAMTS-13 for ELISA may be obtained according to the methods of Non-patent reference 1 and Non-patent reference 8, respectively. A commercially available fluorescently-labeled FRETS-VWF73 (PEPTIDE INSTITUTE, INC.) may be used as a partially synthesized peptide of VWF. The resulting ADAMTS-13 mutant having a higher enzymatic activity than the ADAMTS-13W688X protein is substituted with charged amino acids other than the following amino acids with alanine: aspartic acid at position 343, arginine at position 349, aspartic acid at position 480, arginine at position 488, arginine at position 498, arginine at position 507, aspartic acid at position 533, aspartic acid at position 543, glutamic acid at position 641 and arginine at position 660. The number of substitution of the charged amino acids may be at least one. These ADAMTS-13 mutants may be greatly efficacious at a low dosage in human as a therapeutic agent for e.g. thrombosis. In addition, due to the low dosage, reduction in adverse side effects may be expected.

These effects become immense by the reduced reactivity to a neutralizing autoantibody found in patients with thrombosis in addition to the elevated enzymatic activity. These ADAMTS-13 mutants may be obtained by studying an extent of binding of the ADAMTS-13 mutant having a high enzymatic activity to a neutralizing antibody using ELISA or Western Blotting (hereinafter also referred to as “WB”). The neutralizing antibody as used herein may be a polyclonal antibody or a monoclonal antibody. To obtain the monoclonal antibody, antibody producing cells such as splenocytes or lymphocytes may be collected from an animal immunized with mature dendritic cells from immature dendritic cells, the resulting cells may be fused with myeloma cell line according to Milstein et al., Method Enzymol., 73, 3-46, 1981, to prepare hybridomas which produce an antibody to a specific antigen. Alternatively, an antibody preparation technique using a phage display (Phage Display of Peptides and Proteins: A Laboratory Manual Edited by Brian K. Kay et al., Antibody Engineering: A PRACTICAL APPROACH Edited by J. McCAFFERTY et al., ANTIBODY ENGINEERING second edition edited by Carl A. K. BORREBAECK) may be used to prepare an antibody which binds to a specific antigen. For the above ELISA or WB, the resulting antibody may be labeled by fluorescence labeling, RI, biotinylation, and the like. These are all commercially available as a kit.

The resulting ADAMTS-13 mutant is preferably such that the charged amino acids comprising at least one of arginine at position 312, lysine at position 318, arginine at position 568, glutamic acid at position 569, arginine at position 589, lysine at position 608, glutamic acid at position 634, aspartic acid at position 635 or arginine at position 639 in or around the neutralizing antibody recognition epitope are substituted with alanine. Alternatively, the ADAMTS-13 mutant is preferably such that the charged amino acids selected from the group consisting of aspartic acid at position 298, arginine at position 312, arginine at position 326, glutamic acid at position 327, arginine at position 370, arginine at position 452, aspartic acid at position 504, arginine at position 514, aspartic acid at position 537, arginine at position 568 and arginine at position 659 are substituted. As described above, the number of substitution of the charged amino acids may be 1 or more.

Moreover, the charged amino acids may be substituted with not only alanine as in Examples but also with other uncharged amino acids, preferably glycine, proline, serine and threonine which are subject to easy amino acid substitution during the course of evolution (i.e. analogous amino acids)(BIOINFORMATICS A Practical Guide to the Analysis of Genes and Proteins Edited by ANDREAS D. BAXEVANIS, B. F. FRANCIS OUELLETTE, John Wiley & Sons, Inc.).

The ADAMTS-13 mutant of the present invention may be formulated into a pharmaceutical preparation for treatment, diagnosis or other uses. For example, to prepare a preparation for intravenous administration, a composition may generally be dissolved in an aqueous solution that contains physiologically compatible materials such as sodium chloride, glycine etc. and has a physiologically compatible, buffered pH. A lyophilized formulation may be employed as a final form to enable prolonged stability. A guideline for a composition for intravenous administration is established by the Government's regulation, e.g. “Minimum Requirements for Biological Products”. A pharmaceutical composition of the present invention comprising as an active ingredient the ADAMTS-13 mutant may specifically be used in patients having a reduced ADAMTS-13 level such as patients with disseminated intravascular coagulation (DIC), hemolytic-uremic syndrome (HUS), deep vein thrombosis (DVT), thrombotic thrombocytopenic purpura (TTP), myocardial infarction, pulmonary embolism, cerebral infarction, systemic lupus erythematosus (SLE), and the like. Alternatively said pharmaceutical composition may be used as a supplemental treatment in patients with an elevated blood concentration of VWF, a substrate of this enzyme, or in patients foreseen to develop ULVWF due to inflammation etc.

The present invention is explained by the following Examples which are not construed to limit the present invention. The present invention is specifically exemplified by Examples together with the appended drawings. In Examples, the mutants were expressed in culture supernatant of animal cells (HeLa). Unless otherwise instructed, reagents and devices etc. used for genetic recombination were available from TaKaRa SHUZO, Toyobo, Bio-Rad, PerkinElmer Applied, Beckman and New England Biolabs.

Example 1 Preparation of Alanine Substituents

A DNA comprising the coding region in pCR vector of the gene W688X encoding the minimum unit exerting the ADAMTS-13 activity (ADAMTS-13W688X gene) as described in Patent reference 3 with introduction of FLAG tag sequence at the C-terminal was digested with restriction enzymes XhoI/SalI and extracted. The resulting product was recloned into pKF vector attached to Site-Directed Mutagenesis kit Mutan-Super Express Km (TaKaRa). According to the package insert of the kit, the 5′ phosphorylated synthetic DNA primer sequences listed in tables 1 to 4 were prepared. With these, a total of 78 plasmids were prepared containing the altered ADAMTS-13W688X genes encoding the protein wherein the desired charged amino acids were substituted with alanine. All of the altered ADAMTS-13W688X genes were confirmed by the automatic sequencer CEQ2000XL DNA Analysis System (Beckman). Table 1 shows primers for preparing mutants with substitution in the disintegrin-like domain, Table 2 for primers for preparing mutants with substitution in the cysteine-rich domain, Table 3 for primers for preparing mutants with substitution in the spacer domain, and Table 4 for primers for preparing deglycosylation mutants with substitution in the cysteine-rich and spacer domains. In the primers indicated in the Tables, the numerals on the left are a serial number of the primers and “R287A”, for example, following the period indicates that the amino acid residue arginine (R) at position 287 is substituted with alanine (A). In addition, the mutation site is indicated with lower case in the base sequence.

TABLE 1 SEQ ID NOS: 2-21, left count to right column, respectively, in order of appearance. Primer Base Sequence  1. R287A GACCCGCCGgcGCCTCAACCC  2. D298A CACCCGCCGGcTGCGCAGCC  3. E309A AGCGCCAACGcGCAGTGCCGC  4. R312A GAGCAGTGCgcCGTGGCCTTC  5. K318A TTCGGCCCCgcGGCTGTCGCC  6. R326A ACCTTCGCCgcGGAGCACCTG  7. E327A TTCGCCAGGGcGCACCTGG  8. D330A GAGCACCTGGcTATGTGCCAG  9. D340A TGCCACACAGcCCCGCTGGAC 10. D343A GACCCGCTGGcCCAAAGCAGC 11. R349A AGCTGCAGCgcCCTCCTCGTTC 12. D356A CCTCTCCTGGcTGGGACAGAATG 13. E359A GATGGGACAGcATGTGGCGTG 14. E363A TGTGGCGTGGcGAAGTGGTGC 15. K364A GGCGTGGAGgcGTGGTGCTCC 16. K368A TGGTGCTCCgcGGGTCGCTGC 17. R370A TCCAAGGGTgcCTGCCGCTCC 18. R372A GGTCGCTGCgcCTCCCTGGTG 19. E376A TCCCTGGTGGcGCTGACCCCC 20. R386A GTGCATGGGgcCTGGTCTAGC

TABLE 2 SEQ ID NOS: 22-48, left column to right column, respectively, in order of appearance. Primer Base Sequence 21. R452A CAGTGCGCCgcGACCGACGGC 22. D454A GCCAGGACCGcCGGCCAGCCG 23. R459A CAGCCGCTGgcCTCCTCCCCTG 24. D480A AGCCAAGGGGcTGCTCTGTGC 25. R484A GCTCTGTGCgcACACATGTGC 26. R488A CACATGTGCgcGGCCATTGGC 27. E492A GCCATTGGCGcGAGCTTCATC 28. K497A TTCATCATGgcGCGTGGAGAC 29. R498A ATCATGAAGgcTGGAGACAGC 30. D500A AAGCGTGGAGcCAGCTTCCTC 31. D504A AGCTTCCTCGcTGGGACCCGG 32. R507A GATGGGACCgcGTGTATGCC 33. R514A AGTGGCCCCgcGGAGGACGGG 34. E515A GGCCCCCGGGcGGACGGGACC 35. D516A CCCCGGGAGGcCGGGACCCTG 36. R528A GGCAGCTGCgcGACATTTGGC 37. D533A TTTGGCTGTGcTGGTAGGATG 38. R535A TGTGATGGTgcGATGGACTCC 39. D537A GGTAGGATGGcCTCCCAGCAG 40. D543A CAGGTATGGGcCAGGTGCCAG 41. R544A GTATGGGACgcGTGCCAGGTG 42. D551A TGTGGTGGGGcCAACAGCACG 43. R558A TGCAGCCCAgcGAAGGGCTC 44. K559A AGCCCACGGgcGGGCTCTTTC 45. R566A ACAGCTGGCgcAGCGAGAG 46. R568A GGCAGAGCGgcAGAATATGTC 47. E569A AGAGCGAGAGcATATGTCACG

TABLE 3 SEQ ID NOS: 49-75, left column to right column, respectively, in order of appearance. Primer Base Sequence 48. R589A GCCAACCACgcGCCTCTCTTC 49. R598A TTGGCGGTGgcGATCGGAGG 50. R602A ATCGGAGGGgcCTATGTCGTG 51. K608A GTGGCTGGGgcGATGAGCATC 52. E622A TCCCTCCTGGcGGATGGTCG 53. D623A CTCCTGGAGGcTGGTCGTGTC 54. R625A GAGGATGGTgcTGTCGAGTAC 55. E627A GGTCGTGTCGcGTACAGAGTG 56. R629A GTCGAGTACgcAGTGGCCCTC 57. E634A GCCCTCACCGcGGACCGGCTG 58. D635A CTCACCGAGGcCCGGCTGCC 59. R636A ACCGAGGACgcGCTGCCCCG 60. R639A CGGCTGCCCgcCCTGGAGGAG 61. E641A CCCCGCCTGGcGGAGATCCG 62. E642A CGCCTGGAGGcGATCCGCAC 63. R644A GAGGAGATCgcCATCTGGGG 64. E651A CCCCTCCAGGcAGATGCTGAC 65. D652A CTCCAGGAAGcTGCTGACATC 66. D654A GAAGATGCTGcCATCCAGG 67. R659A CAGGTTTACgcGCGGTATGG 68. R660A GTTTACAGGgcGTATGGCGAG 69. E663A CGGTATGGCGcGGAGTATGG 70. E664A TATGGCGAGGcGTATGGCAAC 71. R670A AACCTCACCgcCCCAGACATC 72. D672A ACCCGCCCAGcCATCACCTTC 73. K681A TTCCAGCCTgcGCCACGGCAG 74. R683A CCTAAGCCAgcGCAGGCCTG

TABLE 4 SEQ ID NOS: 76-79, respectively, in order of appearance. Primer Base sequence 75. N552A GGTGGGGACgcCAGCACGTGC 76. N579A GTTACCCCCgcCCTGACCAG 77. N614A ATCTCCCCTGCCACCACCTAC 78. N667A GAGTATGGCGCCCTCACCCGC

Example 2 Preparation of Vector for Mutant Expression

The expression vector pCAGG (JP Patent 2824434) was digested with SalI and ligated with the plasmid containing the altered ADAMTS-13W688X genes prepared in Example 1 previously cleaved with SalI/XhoI, followed by transformation of E. coli JM109 therewith and incubation on the LB agar medium containing ampicillin to select transformed E. coli cells. The resulting colonies were incubated with a commercially available culture medium overnight, and then extraction and purification were conducted to prepare the desired expression plasmids.

Example 3 Expression in Culture Supernatant and Purification of Mutants

The expression vectors containing the altered ADAMTS-13W688X genes of Example 2 were transfected into HeLa cells using a commercially available Lipofectin reagent. The culture supernatant of temporary expression (15 mL) was collected on Day 3 after the gene transfection. First, Western Blotting was conducted to check whether or not the secretion was present in the culture supernatant by a common procedure using a commercially available antibody to FLAG tag (anti-FLAGM2 monoclonal antibody (SIGMA CORPORATION)). As a result, as showed in FIG. 2, for four alanine substituents: R507A(32), D533A(37) and D543A(40) in the cysteine-rich domain and E641A(61) in the spacer domain, no normal expression in culture supernatant could be found (the numeral in parenthesis of the mutants indicates the primer number; hereinafter the same). The culture supernatants other than these were concentrated to 1 mL using Centriprep YM-10 (Millipore). Due to the FLAG tag sequence possessed by all the mutants at their C-terminal, affinity purification was conducted using agarose gel with an anti-FLAGM2 monoclonal antibody immobilized thereon (SIGMA CORPORATION). The elution was conducted using a FLAG peptide solution at a concentration of 100 μg/mL in accordance with an attached protocol.

Example 4 Measurement of Hydrolytic Activity of Mutants to VWF Partial Peptide Substrate (FRETS-VWF73)

The activity of each of the mutants of Example 3 was measured using the commercially available fluorescent substrate FRETS-VWF73 (PEPTIDE INSTITUTE, INC.). A concentration of the purified protein was normalized by sandwich ELISA using the anti-human ADAMTS-13 rabbit polyclonal antibody described in Non-patent reference 8 and an HRP labeled form of the anti-FLAGM2 murine monoclonal antibody (SIGMA CORPORATION). With this, the fluorescent substrate cleaving activity was measured to quantify the specific activity. Finally, the mutants were evaluated for a relative activity as compared to the specific activity of the wild type W688X with no alanine substitution, the specific activity of which is 1. Thus, it may be concluded that when the relative activity is significantly higher than 1, the mutant will have a higher enzymatic activity than the wild type strain, and when the relative activity is significantly lower than 1, the mutant will have a lower enzymatic activity (or said amino acid is important for exerting the activity).

As a result, as showed in FIG. 3, the amino acid substitutions at position R349 in the disintegrin-like domain and at position R498(29) in the cysteine-rich domain led to the significantly reduced enzymatic activity (the bar graph in FIG. 3 is accompanied by the estimated experimental error of ±20% of this experimental system). On the other hand, the elevated enzymatic activity was observed for the amino acid substitutions at position R326(6), at position R370(17), at position R568(46) and at position R659(67).

Example 5 Measurement of VWF Degrading Activity of Mutants

The activity of each of the mutants of Example 3 was measured as described below using as a substrate the VWF derived from human plasma purified as described in Non-patent reference 1. Referring to Non-patent reference 3, VWF was denatured by incubation with 1.2 M guanidine hydrochloride at 37° C. for 1 h. Then, the VWF was reacted with an appropriate concentration of the ADAMTS-13 mutant at 37° C. for 1 h and the reaction was quenched with EDTA of a final concentration of 5 mM. Thereafter, a degree of cleavage of VWF was measured by collagen binding ELISA (Gerritsen, H E., Turecek, P L., Schwarz, H P., Lammle, B. & Furlan, M.: Assay of von Willebrand factor (vWF)-cleaving protease based on decreased collagen binding affinity of degraded vWF: a tool for the diagnosis of thrombotic thrombocytopenic purpura (TTP). Thromb. Haemost. 82: 1386-1389, 1999). A concentration of the purified protein was normalized by sandwich ELISA using an anti-human ADAMTS-13 rabbit polyclonal antibody described in Non-patent reference 8 and an HRP labeled form of an anti-FLAGM2 murine monoclonal antibody (SIGMA CORPORATION). With these, the fluorescent substrate cleaving activity was measured to quantify the specific activity. Finally, the mutants were evaluated for a relative activity as compared to the specific activity of wild type W688X with no alanine substitution, the specific activity of which is 1. Thus, it may be concluded that when the relative activity is significantly higher than 1, the mutant will have a higher enzymatic activity than the wild type strain, and when the relative activity is significantly lower than 1, the mutant will have a lower enzymatic activity (or said amino acid is important to exerting the activity).

As a result, as showed in FIG. 4, the substitutions at position R326(6), at position D330(8), at position D343(10) and at position R349(11) in the disintegrin-like domain, at position D480(24), at position R488(26) and at position R498(29) in the cysteine-rich domain, and in the vicinity of position R660(68) in the spacer domain led to the reduced binding ability to VWF. On the other hand, the substitutions at position D298(2) and at position E327(7) in the disintegrin-like domain, at position R452(21), at position D504(31), at position R514(33) and at position D537(39) in the cysteine-rich domain led to the enhanced VWF cleaving activity (the bar graph in FIG. 4 is accompanied by the estimated experimental error of ±20% of this experimental system).

Example 6 Evaluation of Mutants for their Binding Ability to VWF

Each of the purified mutants of Example 3 was evaluated for their binding ability to VWF derived from human plasma immobilized on ELISA plate as described in Non-patent reference 8. The concentration was normalized by sandwich ELISA using the anti-human ADAMTS-13 rabbit polyclonal antibody and an HRP labeled form of the anti-FLAGM2 murine monoclonal antibody (SIGMA CORPORATION) as described above and the VWF binding ability per unit concentration was quantified. Finally, the mutants were evaluated for a relative activity as compared to the specific activity of wild type W688X with no alanine substitution, the specific activity of which is 1. Thus, it may be concluded that when the relative activity is significantly higher than 1, the mutant will have a higher affinity than the wild type strain, and when the relative activity is significantly lower than 1, the mutant will have a lower affinity (or said amino acid is important for the recognition of VWF).

As a result, as showed in FIG. 5, the substitutions at position D343(10) and at position R349(11) in the disintegrin-like domain, at position D480(24), at position R488(26) and at position R498(29) in the cysteine-rich domain and at position R660(68) in the spacer domain led to the reduced binding ability to VWF. On the other hand, the substitutions at position E327(7) in the disintegrin-like domain led to the enhanced affinity to VWF (the bar graph in FIG. 5 is accompanied by the estimated experimental error of ±20% of this experimental system).

Example 7 Epitope Analysis of Neutralizing Antibody 1

Following the Western Blotting (WB) in Example 3 to confirm the expression, the anti-FLAG antibody was released by a WB separating solution (NAKARAI), reacted again with the murine monoclonal antibodies (WH2-22-1A, W688X6-1 and W688X3-69) having an ability to neutralize the ADAMTS-13 activity established by the present inventor using common procedures as described in Non-patent reference 8, and visualized with an HRP labeled form of the anti-murine immunoglobulin (VECTOR) wherein the epitopes of the antibodies were confirmed by a reduced color intensity (FIG. 6). As a result, it was revealed that the vicinity of R312 and K318 for WH2-22-1A, the vicinity of R568 and E569 for W688X6-1 and the vicinity of R589 and D635 for W688X3-69 were recognized as an epitope. In addition, it was revealed that these amino acid residues recognized as an epitope were different from the amino acid residues thought to be important for the activity to hydrolyze FRETS-VWF73 and for the binding to VWF. It was suggested that the altered molecule having a reduced reactivity to antibodies from patients may be designed by this method without affecting the enzymatic activity through the epitope analysis of neutralizing antibodies from patients.

Example 8 Epitope Analysis of Neutralizing Antibody 2

Following the WB (under non-reducing condition) to confirm the expression in Example 3, the anti-FLAG antibody was released with a WB releasing solution (NAKARAI), in a similar way to Example 7, reacted again with immunoglobulin G (IgG) fractions isolated from acquired TTP patients having the ability to neutralize the ADAMTS-13 activity, and visualized with an HRP labeled form of the anti-human immunoglobulin (Dako) wherein the epitopes of the antibodies were confirmed by a reduced color intensity (FIGS. 7 to 9). As a result, it was suggested that the vicinity of K608, E634, D635, E642 and R644 in the spacer domain and N578, N614 and N667 in the glycosylation site were recognized as an epitope. In addition, it was revealed that these amino acid residues recognized as an epitope were different from the amino acid residues thought to be important for the activity to hydrolyze FRETS-VWF73 and for the binding to VWF. Therefore, the substitution of these major epitope amino acids with different amino acids allows for preparing altered molecules having the reduced reactivity to antibodies from patients while the enzymatic activity is maintained or even enhanced like the mutant of E327.

Example 9 Evaluation of Mutants with Reduced Reactivities with Antibodies from Patients

The reactivity of the mutants, which were estimated from the result of Example 8 to have the reduced reactivity with autoantibodies from acquired TTP patients (K608A, E634A, D635A, E642A, R644A, and glycosylation site N578A, N614A, N667A), with the autoantibodies was evaluated using the commercially available fluorescent substrate FRETS-VWF73(PEPTIDE INSTITUTE, INC.) (FIG. 10). The cleaving activity of the ADAMTS-13 mutants to the FRETS-VWF73 fluorescent substrate per 1 min. (AFU/min) was measured with and without addition of antibodies from patients A, B and C (Ab+/−) to select mutants having a sufficient enzymatic activity even when a neutralizing antibody from the patients is added (i.e. the enzymatic activity kept at 50% or more of that of without addition of the neutralizing antibodies). As a result, it was revealed that depending on patient antibody, K608A, E634A and D635A had a sufficient enzymatic activity. In addition, K608A was revealed to have a sufficient enzymatic activity to all the patient antibodies.

Therefore, the substitution of these major epitope amino acids with different amino acids which reduce the antibody reactivity allows for preparing altered molecules (e.g. double mutant such as E327A/K608A) having the reduced reactivity to antibodies from patients while the enzymatic activity is maintained or even enhanced like the E327 mutant.

INDUSTRIAL APPLICABILITY

The ADAMTS-13 mutant of the present invention may be used as a medicament significantly efficacious as a supplemental treatment to thrombotic disease such as TTP. 

The invention claimed is:
 1. A method of reducing reactivity of ADAMTS-13 (a disintegrin-like domain, and metalloprotease) to an anti-ADAMTS-13 neutralizing antibody, with an isolated human thrombospondin type 1 motif, member 13, the method comprising substituting the following positions in the isolated human ADAMTS-13 with a different charged or uncharged amino acid: arginine at position 326, aspartic acid at position 330, aspartic acid at position 343 and arginine at position 349 in the disintegrin-like domain, aspartic acid at position 480, arginine at position 488, arginine at position 498, arginine at position 507, aspartic acid at position 533 and aspartic acid at position 543 in the cysteine-rich domain, and glutamic acid at position 641 and arginine at position 66o in the spacer domain, in the amino acid sequence encoded by the nucleotide sequence of SEQ ID NO:
 1. 2. The method according to claim 1, wherein the different amino acid is an uncharged amino acid.
 3. The method according to claim 1 wherein the charged amino acid to be substituted is present in or around the neutralizing antibody recognition epitope, including at least one of arginine at position 312, lysine at position 318, arginine at position 568, glutamic acid at position 569, arginine at position 589, lysine at position 608, glutamic acid at position 634, aspartic acid at position 635 or arginine at position
 639. 4. The method according to claim 1, wherein the charged amino acid to be substituted is selected from the group consisting of aspartic acid at position 298, arginine at position 312, arginine at position 326, glutamic acid at position 327, arginine at position 370, arginine at position 452, aspartic acid at position 504, arginine at position 514, aspartic acid at position 537, arginine at position 568 and arginine at position
 659. 5. The method according to claim 1, wherein the uncharged amino acid is selected from the group consisting of alanine, glycine, proline, serine and threonine. 